Thin film magnetic recording media

ABSTRACT

A method and apparatus for forming a thin film magnetic recording media, the method comprises generating magnetic nanoclusters from a target of magnetic material, crystallizing the magnetic nanoclusters, and depositing the magnetic nanoclusters onto a substrate to form a thin film of magnetic particles thereon. The magnetic nanoclusters are deposited onto the substrate after crystallized and therefore after the deposition. The apparatus comprises a first chamber, a second chamber connected to the first chamber, and a third chamber connected to the second chamber. The first chamber has a source for generating magnetic nanoclusters. The second chamber is to receive the magnetic nanoclusters and crystallize the magnetic nanoclusters. The third chamber is to receive the crystallized magnetic nanoclusters from the second chamber and deposit the crystallized magnetic nanoclusters onto the substrate positioned therein.

FIELD OF THE INVENTION

The present invention relates to magnetic recording media. Inparticular, it relates to thin film magnetic recording media for datastorage devices.

BACKGROUND OF THE INVENTION

The rapid development of computer and information technology hasresulted in great demand for high capacity storage devices. Currently,these storage devices are being pushed to their limits by applicationsas diverse as digital video editing and genomics. Therefore, the datastorage industry is continually under pressure to increase the capacityof data storage devices. One of the primary methods to increase capacityis to increase the recording density of the magnetic recording media inmost storage devices. To achieve an ultra-high recording density of, forexample, about 100 Gbits/inch² or higher, magnetic recording media arerequired to possess a low remnant-thickness product (Mrδ), a highcoercivity (Hc) as well as a high signal-to-media noise (S/Nm).

In a conventional magnetic recording media, such as a Cobalt (Co) basedalloy, non-magnetic elements such as Chromium (Cr) and/or Boron (B) areincorporated into the thin film magnetic recording media to reduce thegrain size as well as to reduce the intergranular coupling effect of themagnetic particles in the recording media. The result is a magneticrecording medium having a grain size of about 8-12 nanometers (nm) witha distribution width of about 20% or more. In this context, the term“distribution width” denotes the Full Width at Half Maximum (FWHM)height of the grain size distribution.

In order to obtain a high S/N_(m) magnetic recording media, the grainsize and their distribution width as well as the intergranular couplingbetween the magnetic grains must be properly controlled to further scaledown.

Reduction of grain size for Co-based alloy recording media is limited bythe thermal-instability of the magnetic grains or particles, commonlyreferred to as the “superparamagnetism” effect. Attempts to overcomethis limitation are illustrated in “Effect Of Magnetic AnisotropyDistribution In Longitudinal Thin Film Media” by Hee et al (J. Appl.Phys., Volume 87, 5535-5537, 2000) and U.S. Pat. No. 6,183,606 to Kuo etal. The Hee article discloses a method using highly oriented media toallow further reduction of the grain size. In contrast, the Kuo patentuses L1₀ ordered FePt or CoPt material to form longitudinal orperpendicular magnetic recording media with very small magneticallystable grains.

While the above methods provide possibilities to obtain magneticallystabled grains with further reduced size in a first place, in thesubsequent post-deposition annealing process, a high temperature, forexample 600° C. or above, is to apply to the substrate in order toobtain recording media with an appropriate crystallized structure orwith chemically ordered L1₀ FePt or CoPt. Unfortunately, this hightemperature annealing process also increases grain size from about 10nanometers (nm) to about 30 nm in the deposited thin film, whicheventually reduces the recording density. In addition, no solution isprovided by these methods to control the grain distribution width. Dueto the larger grain size and their wide distribution width, these filmshave presented rather poor recording properties, in particular a verylow S/N_(m). Moreover, the high-temperature annealing process is notcompatible with existing magnetic recording media fabrication processand materials.

SUMMARY OF THE INVENTION

The present invention seeks to provide a method and apparatus forforming thin film magnetic recording media with higher recording densityby virtue of the reduced grain size and distribution width. The presentinvention also provides a thin film magnetic recording medium formedaccordingly. The present invention successfully eliminates the postannealing process necessary for the conventional methods as thedeposition is done after the magnetic particles are crystallized,therefore avoids the grain growth after the formation of the thin filmmagnetic recording media by heating up the substrate for annealingpurpose. According to the present invention, the magnetic easy axis ofthe magnetic particles are finely controlled during the depositionprocess and further, the magnetic particles are well isolated from eachother either before or during the deposition process.

In accordance with a first aspect of the present invention, there isprovided a method for forming a thin film magnetic recording media, themethod comprises generating magnetic nanoclusters from a target ofmagnetic material, crystallizing the magnetic nanoclusters, anddepositing the magnetic nanoclusters onto a substrate to form a thinfilm of magnetic particles thereon. The magnetic nanoclusters aredeposited onto the substrate after crystallized and therefore after thedeposition, it is unnecessary to heat up the substrate.

In accordance with a second aspect of the present invention, there isprovided an apparatus for forming a thin film magnetic recording mediaonto a substrate. The apparatus comprises a first chamber, a secondchamber connected to the first chamber, and a third chamber connected tothe second chamber. The first chamber has a source for generatingmagnetic nanoclusters. The second chamber is to receive the magneticnanoclusters and crystallize the magnetic nanoclusters. The thirdchamber is to receive the crystallized magnetic nanoclusters from thesecond chamber and deposit the crystallized magnetic nanoclusters ontothe substrate positioned therein.

In accordance with a third aspect of the present invention, there isprovided a thin film magnetic recording medium, the medium comprises anon-magnetic substrate and a magnetic thin film layer disposed on thesubstrate. The magnetic thin film layer comprises magnetic particlesisolated by a non-magnetic material, and the magnetic particles areformed on the substrate after crystallized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an enlarged cross sectional view showing a thin film magneticrecording medium according to one embodiment of the present invention.

FIG. 1B is an enlarged cross sectional view showing a thin film magneticrecording medium according to another embodiment of the presentinvention.

FIG. 2A is an enlarged top view showing a parallel magnetizationorientation of the magnetic nanoparticles formed according to oneembodiment of the present invention.

FIG. 2B is an enlarged top view showing a circumferential magnetizationorientation of the magnetic nanoparticles formed according to anotherembodiment of the present invention.

FIGS. 3A and 3B are enlarged cross sectional views showing perpendicularmagnetization orientations of the magnetic nanoparticles formedaccording to the present invention.

FIG. 4 is a schematic diagram showing an apparatus for forming magneticthin film onto a substrate according to one embodiment of the presentinvention.

FIGS. 5A, 5B and 5C are schematic diagrams showing variousconfigurations of the magnetic field according to the present invention.

FIG. 6 is a schematic diagram showing an apparatus for forming magneticthin film onto a substrate according to another embodiment of thepresent invention.

FIG. 7 is a schematic diagram showing an apparatus for forming magneticthin film onto a substrate according to a further embodiment of thepresent invention.

FIG. 8 is a flow chart showing a method for forming magnetic thin filmonto a substrate according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A illustrates a thin film magnetic recording medium formedaccording to one embodiment of the present invention. The thin filmmagnetic recording medium 100 comprises a substrate 110, a thin filmmagnetic layer 120 deposited onto the substrate 110 and a protectiveovercoating 130 deposited on the thin film magnetic layer 120. Thesubstrate 110 may be formed of a non-magnetic material such as silicon,glass, or aluminum alloy. The thin film magnetic layer 120 comprises aplurality of magnetic particles 122. Examples of magnetic materials thatmay be used to form magnetic particles 122 include Co, Fe, Ni, Sm, Pt,Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W, Mo, Ag, Ru, Au, Nb, Pb, Dy, abinary alloy of aforesaid elements, a ternary alloy of said elements, anoxide of Fe further comprising at least one of the said elements otherthan Fe, barium ferrite and strontium ferrite, carbide and nitride ofthe said elements. The preferred magnetic materials are, for example,CoPt, FePt or CoPd.

The magnetic particles 122 are encapsulated by non-magnetic material 124a. The magnetic particles 122 are oriented with its magnetic easy axis126 aligned parallel to a surface 114 of the substrate 110. In FIG. 1B,the magnetic particles 122 are disposed on the substrate 110simultaneously with a non-magnetic material 124 b, such that themagnetic particles 122 are dispersed within the non-magnetic material124 b. It should be appreciated that the intergranular coupling effectof the magnetic particles isolated by the non-magnetic material 124 a(FIG. 1) and 124 b (FIG. 2) in the above structure can be effectivelyreduced.

FIGS. 2A and 2B show two examples of the highly oriented alignment ofmagnetic easy axis of the magnetic particles in the magnetic thin filmfor longitudinal recording media. FIG. 2A shows that the magnetic easyaxes 226 a of the magnetic particles 222 are parallel to the surface ofthe substrate 210. FIG. 2B shows that the magnetic easy axes 226 a ofthe magnetic particles 222 are parallel to the surface of the substrate210 and are circumferentially aligned.

FIG. 3A illustrates a thin film magnetic recording medium formedaccording to another embodiment of the present invention. The thin filmmagnetic recording medium 300 comprises a substrate 310, a thin filmmagnetic layer 320 deposited onto the substrate 110 and a protectiveovercoating 330 deposited on the thin film magnetic layer 120. Thesubstrate 110 may be formed of a non-magnetic material made of, forexample, a silicon wafer, glass or aluminum alloy. The thin filmmagnetic layer 320 includes a plurality of magnetic particles 322comprising magnetic materials, such as Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd,Pd, Gd, B, N, C, P, Ti, W, Mo, Ag, Ru, Au, Nb, Pb, Dy, a binary alloy ofaforesaid elements, a ternary alloy of said elements, an oxide of Fefurther comprising at least one of the said elements other than Fe,barium ferrite and strontium ferrite, carbide and nitride of the saidelements.

The magnetic particles 322 are encapsulated by a layer of non-magneticmaterial 324 a according to the method illustrated below, and with itsmagnetic easy axis 326 aligned perpendicular to the surface 314 of thesubstrate 310. In FIG. 3B, the magnetic particles 322 are disposed onthe substrate 310 simultaneously with a non-magnetic material 324 b,such that the magnetic particles 322 are dispersed within thenon-magnetic material 324 b.

As shown in FIG. 4, an apparatus for forming magnetic thin film onto asubstrate according to one embodiment of the present invention comprisesa cluster-forming chamber 410, a heating chamber 420, an encapsulationchamber 429 and a deposition chamber 430. The cluster-forming chamber410 comprises a target 416 made of a magnetic material selected from,for example, Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W,Mo, Ag, Ru, Au, Nb, Pb, Dy, a binary alloy of aforesaid elements, aternary alloy of said elements, an oxide of Fe further comprising atleast one of the said elements other than Fe, barium ferrite andstrontium ferrite, carbide and nitride of the said elements. Thecluster-forming chamber 410 comprises a power unit 412 connected to ananode 413 and the target 416 (which is used as a cathode). Thecluster-forming chamber 410 also includes a first conduit 411 forsupplying a first gas, such as argon (Ar) and a second conduit 415 forsupplying a second gas such as helium (He). The Ar serves as bothsputtering gas and aggregation gas while the He is used to control thecluster size and initial distribution width due to its highheat-transfer ability. A liquid nitrogen cooling unit 414 is alsoprovided for promoting the formation of the cluster with desired size.Examples of the power unit 412 are a direct current (DC) or radiofrequency (RF) power supply. The cluster-forming chamber 410 preferablyoperates at a working pressure in a range of about 0.1 Torr to 1 Torr,which is higher than that of the conventional sputtering pressure. Thepurpose of using a pressure for sputtering in this level is to providemore collision chance of the particle and to form large particle. Theparameters of controlling the particle size include gas pressure, gasflow rate, ratio of Ar and He. A diaphragm 417 is provided at one end ofthe nitrogen cooling unit. Another diaphragm 418 is provided to connectthe cluster-forming chamber 410 and the heating chamber 420.

Pumping systems 433, 434, and 435 are provided for adjusting thepressure of the cluster-forming chamber 410, the encapsulation chamber429 and the deposition chamber 430. The pressure of the depositionchamber 430 is maintained at a level lower than the pressure of theother two chambers to enable cluster transportation from thecluster-forming chamber 410 to the deposition chamber 430. The pressurerange of the cluster-forming chamber 410, the encapsulation chamber 429and the deposition chamber 430 can be set to about 0.1-1 Torr, 10⁻⁴Torr, and 10⁻⁶ Torr, respectively.

At the start of the process, energized argon gas ions (Ar+) areaccelerated towards the target 416 to eject atoms 421 from the target 16upon impact. The ejected atoms 421 are then decelerated by collisionwith the argon gas (Ar+) and start to agglomerate to form clusters. Theliquid nitrogen cooling unit 414 and helium supplied from the conduit415 aid in cooling the ejected atoms 421 to form a set of clusters 422.

After being exposed to the noble gases (Ar+), the clusters 422 then movethrough the diaphragm 417 and agglomerate together to form a set oflarger clusters 423, which continue move onwards to the heating chamber420 through diaphragm 418, and further form final clusters 424 in theheating chamber 420. The clusters 424 may consist of several hundredmagnetic atoms up to several million magnetic atoms, which are looselybonded with each other. In the process, atoms are agglomerated togetherto form clusters, and more atoms are attached to the boundary portionsof the clusters continuously. As a result, the clusters will be formedwith larger sized agglomerates located at the center portion and withrelatively smaller sized agglomerates locates at the boundary portion.Upon passing through the diaphragm 418, smaller sized agglomerateslocated at the boundary portions of the clusters 423 can be trimmed offby the diaphragm. As a result, the clusters 424 passing through thediaphragm will have the smaller sized agglomerates removed. Therefore,clusters with a distribution width smaller than that of the clusters 423before the diaphragm 418 can be obtained. In this embodiment, thedimension of the clusters 424 is in a range of about 1 nm to 20 nm and adistribution width of about 10% or less.

It should be appreciated according to the above illustration thatvarious parameters may be adjusted to control the dimension anddistribution width, including the pressure of the cluster-formingchamber 410, the sputtering rate of the target materials, the ratio ofthe helium to other noble gases, the distance between the target 416 andthe diaphragm 417 and the size of the diaphragms 417 and 418, etc.

The apparatus further comprises a number of heaters 419 for heating thegas-phase clusters 424 to a temperature of about 900° C. to achievecrystallization. Examples of the heaters 419 include a resistancefurnace heater or a lamp heater. After heating, the clusters 424 areconverted into crystallized magnetic nanoclusters 425 with a desiredcrystalline structure for data storage purpose.

The magnetic nanoclusters 425 are then moved to the encapsulationchamber 429. A surfactant 427 is then supplied to the encapsulationchamber by a spray nozzle 428, such as a nebuliser. The surfactant ispreferably a material which can be absorbed by the magnetic nanocrystals425 to form encapsulated magnetic nanocrystals 426. The surfactant 427may be selected from a group of organic materials, including fattyacids, alkyl thiols, alkyl diulfides, alkyl nitrites and alkylisonitiles, which is an end group that is attracted to the magneticnanocrystals 425. The surfactant may also be a methylene having a chain8 to 12 units long, which provides steric repulsion to prevent themagnetic nanocrystals 425 from adhering to the substrate in thesubsequent deposition process. The term “8 to 12 units long” denotesthat for polymer materials, its structure is chain-like, for example “8unit” refer to the chain structure of C—C—C—C—C—C—C—C (C means carbon,other bonds of carbon bond to the function group such as hydrogen, —OHetc.)

The encapsulated magnetic nanocrystals 426 are then transported into thedeposition chamber 430 to be deposited onto the substrate 431. Asillustrated above, because the magnetic nanocrystals 425 arecrystallized before reaching the substrate 431, the magneticnanocrystals 425 are usually a single domain. Because the energy of themagnetic nanocrystals 425 is very low, the encapsulated magneticnanocrystals 426 will remain intact after deposition onto the substrate.

An external magnetic field 432 is provided adjacent to the substrate431, which forms a relatively uniform magnetic field direction asillustrated in FIG. 4. When the encapsulated magnetic nanoclusters 426reach the substrate 431, they will be aligned by following the directionof the magnetic field 432 whilst depositing on the substrate 431. Themagnetic thin firm can then be formed with highly oriented magnetic easyaxis along a predetermined direction controlled by the magnetic field432.

FIGS. 5A and 5B show alternative configurations of a magnetic fieldadjacent to a substrate for aligning the orientation of the magneticparticles. In FIG. 5A, two permanent magnets or electromagnets 537 a and537 b are placed underneath a substrate 531. The north magnetic pole ofmagnet 537 a and the south magnetic pole of magnet 537 b are placedadjacent to the substrate 530 to generate a magnetic field 520. Themagnetic field 520 aligns the magnetic particles along a directionparallel to the top surface 531 a of the substrate 531 duringdeposition. In addition, the substrate 531 and the magnets 537 a, 537 bmay be rotated during the deposition process to achieve uniformity ofthe magnetic thin film deposition.

As shown in FIG. 5B, a circumferentially-oriented magnetic field 540 maybe obtained by passing through an electrical wire 538 through the centerof the substrate 531. The magnetic field 540 aligns the magneticclusters during deposition along a direction parallel to andcircumferential with respect to the a top surface 531 a of the substrate531.

As shown in FIG. 5C, a magnetic field 560 with a direction perpendicularto a top surface 531 a of the substrate 531 may be obtained by placing asolenoid 539 around the substrate 531. The solenoid aligns the magneticparticles during deposition along a direction perpendicular to thesubstrate surface. It should be appreciated that magnetic thin filmshaving different magnetic orientations may be obtained by applying anappropriate magnetic field adjacent to the substrate.

FIG. 6 shows an apparatus for forming magnetic thin film onto asubstrate according to another embodiment of the present invention. Theapparatus comprises a cluster-forming chamber 610, a heating chamber620, an encapsulation chamber 629, and a deposition chamber 630. In thisembodiment, the encapsulation chamber 629 is coupled between thecluster-forming chamber 610 and the heating chamber 620.

The loosely bonded magnetic nanoclusters 624 formed by thecluster-forming chamber 610 are transported into the encapsulationchamber 629. A spray of organic solvent or surfactant 627 are suppliedby the nozzle 628 into the encapsulation chamber 629 to mix with themagnetic nanoclusters 624 to form the encapsulated nanoclusters 625.

The encapsulated nanoclusters 625 are transported into the heatingchamber 620 thereafter. The encapsulated nanoclusters 624 a are heatedby the heaters 619 to a temperature of about 900° C. to form crystalizedmagnetic nanoclusters 626. At the same time, the organic materialsencapsulating the nanoclusters will be carbonized by the heatingprocess, therefore the crystallized magnetic nanoclusters 626 areencapsulated with a layer of amorphous carbon. The encapsulated magneticnanoclusters are then deposited onto the substrate 631 located in thedeposition chamber 630.

FIG. 7 shows an apparatus for forming magnetic thin film onto asubstrate according to a further embodiment of the present invention.The apparatus comprises a cluster-forming chamber 710, a heating chamber720 and a deposition chamber 730. In this embodiment, the loosely bondedmagnetic nanoclusters 724 are formed in the cluster-forming chamber 710,and transported into the heating chamber 720.

After heating in the heating chamber 720, the loosely bondednanoclusters 724 become close-packed and crystallized magneticnanoclusters 725. The magnetic nanoclusters 725 are then transportedinto the deposition chamber 730 to be deposited onto substrate 731. Atthe same time, non-magnetic materials are also deposited onto thesubstrate 731 by a source 736. Examples of non-magnetic materials thatmay be used include C, SiO₂, Si₃N₄ BN and/or carbon hydrogenate polymer.

FIG. 8 shows a method 800 for forming a thin film magnetic recordingmedia according to the present invention. In a first block 802, magneticnanoclusters are generated from a target. In a next block 804, themagnetic nanoclusters are heated to a crystallization temperature,whereby the magnetic nanoclusters are crystallized so that to processnecessary properties for data storage purpose. Thereafter in a furtherblock 806, the crystallized magnetic nanoclusters mixed up with anon-magnetic material. The non-magnetic material encapsulate thecrystallized magnetic nanoclusters and therefore, the intergranularcoupling effect of the magnetic particles will be reduced. In a nextblock 808, the encapsulated magnetic nanoclusters are disposed onto asubstrate to form solid-phase magnetic particles.

It should be appreciated that according to the above method, since thedesired crystalline structure are obtained before deposition, thesubstrate after the magnetic nanoclusters deposited thereon needs not beheated up for annealing purpose. Accordingly, the grain growth by thepost-deposition annealing is successfully eliminated.

1-17. (canceled)
 18. An apparatus for forming a thin film magneticrecording medium onto a substrate, the apparatus comprising: a firstchamber having a source for generating magnetic nanoclusters; a secondchamber connected to the first chamber for receiving and crystallizingthe magnetic nanoclusters, a third chamber connected to the secondchamber for receiving the crystallized magnetic nanoclusters anddepositing the crystallized magnetic nanoclusters onto the substratepositioned therein, wherein the magnetic nanoclusters are deposited onthe substrate after crystallized.
 19. The apparatus as recited in claim18, further comprising a first supplier for providing a firstnon-magnetic material to encapsulate the magnetic nanoclusters.
 20. Theapparatus as recited in claim 19, wherein the first non-magneticmaterial comprises a surfactant.
 21. The apparatus as recited in claim20, wherein the surfactant comprises at least one of a group consistingof fatty acids, alkyl thiols, alkyl diulfides, alkyl nitrites and alkylisonitiles.
 22. The apparatus as recited in claim 18, further comprisinga rotatable stage for holding the substrate in the third chamber. 23.The apparatus as recited in claim 18, further comprising a secondsupplier for depositing a second non-magnetic material onto thesubstrate upon deposition of the magnetic nanocrystals.
 24. Theapparatus as recited in claim 23, wherein the second non-magneticmaterial comprises at least one of a group consisting of C, SiO₂, Si₃N₄,BN and carbon hydrogenate polymer.
 25. The apparatus as recited in claim48, wherein the magnetic material comprises at least one of a groupconsisting of Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W,Mo, Ag, Ru, Au, Nb, Pb, Dy.
 26. The apparatus as recited in claim 25,further comprising at least one of a group consisting of a binary alloyand a ternary alloy of the magnetic material.
 27. A thin film magneticrecording medium comprising: a substrate; a magnetic thin film layerdisposed on the substrate, wherein the magnetic thin film layer hasmagnetic particles isolated by a non-magnetic content, wherein themagnetic particles are formed on the substrate after crystallization.28. The thin film magnetic recording medium as recited in claim 27,wherein each of the magnetic particles has a magnetic easy axis that isanisotropically orientated.
 29. The thin film magnetic recording mediumas recited in claim 27, wherein the magnetic particles having adimension of less than about 8 nm.
 30. The thin film magnetic recordingmedium as recited in claim 29, wherein the magnetic particles having adistribution width of less than about 10%.
 31. The thin film magneticrecording medium as recited in claim 27, wherein the non-magneticcontent comprises at least one of a group consisting of fatty acids,alkyl thiols, alkyl diulfides, alkyl nitrites and alkyl isonitiles. 32.The thin film magnetic recording medium as recited in claim 27, whereinthe non-magnetic content comprises at least one of C, SiO₂, Si₃N₄, BNand carbon hydrogenate polymer.
 33. The thin film magnetic recordingmedium as recited in claim 27, further comprising a protectiveovercoating disposed on the magnetic thin film layer.